I have two SB-600 speedlights, and now I'm about to invest in some accessories - including an umbrella. Here's the thing: I don't have any light stands - nor do I want them, at least not for now. I much prefer to "stay mobile", and I find that tripods are quite limiting when it comes to that.

However, the convenient thing with light stands and umbrella adapters is that you have something to hold the umbrella in a "correct" position. My question is this: Is it possible to simply use a rubber band to attach the umbrella to the top of my flash? Or will I totally screw up the light if I do it this way?

By simply putting the umbrella on top of my flash, I'm thinking that I'd be able to move around more freely, without carrying light stands all the time...And save some money as well

I'd say you can use 2 rubber bands if you have a relatively light umbrella, but for the heavier ones I think you will need a stand. Also, keep in mind that you lose a lot of light with an umbrella. A softbox will be a more efficient, albeit more expensive solution.

_________________I take pictures so quickly, my highschool was "Continuous High".

I have a feeling you're not going to get sufficient coverage if you simply 'rubber band' an umbrella to the top of your flash; it'd probably only hit the bottom half of the umbrella.

If you're going to use it for running and gunning, have you considered alternatives such as Westcott's Mini Apollo or Lumiquest's Softbox III? They're probably not going to be as effective as an umbrella, but they're more non-light stand friendly.

Otherwise, I'd assume that you would have time to prepare/make adjustments, in which case I'd suggest you just man up and get a half decent light stand (they're not ridiculously expensive). They're not exactly that hard to move around and adjust, especially if it's just a speedlight and umbrella.

If you have someone helping you and you have a lot of cash to burn (which I doubt, since you're trying to save money), you could invest in Lastolite's Ezybox, which has the option of an extending handle that an assistant can use to position the softbox for you.